Gas-blast circuit-breakers operating with extinguishing gas consisting of or comprising a fluorinated compound



United States Patent Inventor Rintje Boersma Ilarmelen, NetherlandsAppLNo; 691,012 Filed Dec. 15, 1967 Patented Dec. 1, 1970 AssigneeN.V.COQ

Utrecht, Netherlands a Dutch limited liability company Priority Dec. 28,1966 Netherlands 6618237 Pat. 1]

GAS-BLAST CIRCUIT-BREAKERS OPERATING WITH EXTINGUISHING GAS CONSISTINGOF OR COMPRISING A FLUORINATED COMPOUND 11 Claims, 2 Drawing Figs.

200/144, 200/149 Int. Cl 1-l0lh 33/60 Field of Search 200/ 1 48.7,

144.3, 148.5, 148, 149.1, (Cursory) Primary Examiner-Robert S. MaconArtorneylmirie, Smiley, Snyder and Butrum ABSTRACT: The portions of agas blast circuit breaker employing a fluorinated insulating gas, suchas the contacts and parts adjacent thereto and surfaces of theextinguishing chamber, which are disposed in close adjacency to the areproduced by opening the contacts, are made of a sintered tungsten-nickelalloy consisting essentially of from 95-99] percent tungsten and thebalance nickel. These portions are also coated in part with carbon.

GAS-BLAST CIRCUIT-BREAKERS OPERATING WITH EXTINGUISHING GAS CONSISTINGOF OR COMPRISING A FLUORINATED COMPOUND The invention relates to agas-blast circuit breaker, in which the electric arc setup during theswitching-off process is extinguished by a blast of gas consisting of orcomprising a fluorinated compound, such as sulfur hexafluoride,

It is known that the extinguishing action of certain gaseous fiuorinatedcompounds is very much stronger than that of air or nitrogen, so thatfor the extinguishing process considerably less gas is required However,a disadvantage of these fluorinated compounds is that they dissociateunder the infiuence of the electric arc and that several dissociationproducts thereof are very aggressive and are apt to attack the'materials used in the circuit breaker and are liable to form compoundswith several metals among these materials which settle in powdered formwithin the confines of the circuit breaker. These powdered substancescan be very hygroscopic so that, for instance during inspection of theinner parts of the circuit breaker, water vapour contained in the air istaken up and thereby forms a conductive layer on the surface of theinsulators. Additionally, corrosive agents such as hydrofluoric acid maybe formed. It has already been proposed to conduct the flow of gaseousand powdered switching products, immediately after their having passedthe arc-extinguishing chamber, through filters which render theaggressive products chemically harmless and collect the powderedsubstances, but in that case the switching contacts, the arcing contactsand the walls of the arc-extinguishing chamber of the circuit breakerare often soon covered with a chemically aggressive layer, so that acircuit breaker of this kind will have to be opened and cleaned directlyafter it has been switched off. Moreover, in such a circuit breaker thefilters are mounted in the vicinity of the live parts of the circuitbreaker which makes the replacement of the filter material difficult.Furthermore, these filters must have large filtering areas since thequantity of gas used to extinguish the arc must be passed through saidfilters in the very short space of time involved in the switchingprocess. Such filters require a considerable enlargement of thedimensions of the circuit breaker.

An object of the invention is to avoid entirely or almost entirely thedisadvantages of the known circuit breakers of the mentioned kind. It ischaracterized in that at least each of the surfaces of the circuitbreaker parts lying, during the switching-off process, within the activeradiation field of or which come into contact with the arc and/or theconstituents of the very hot gas mixture produced by dissociation of apart of the extinguishing gas heated by said are, is constituted ofmaterial which guarantees that at the pressures and the temperaturesobtaining on said surfaces during the switching process, only negligibleor almost negligible quantities of deleterious gaseous or solid productsare formed. The invention is based on the recognition that greatadvantages can be achieved if the circuit breaker parts, such as thearcing contacts and the wall parts of the arc-extinguishing chamberwhich lie in the direct vicinity of the arc and the parts at greaterdistances from the electric are are manufactured of or clad withmaterials whichform with said dissociation products mainly nonaggressiveproducts. Those very few aggressive products which may appear eitherremain gaseous under the I circumstances obtaining in the circuitbreaker or, if solid, are

of negligible quantity and in the form of powdered metal fluorides whichare either nonhygroscopic or substantially nonhygroscopic. The resultthereof is that in many cases the filters may be omitted or, if stilldesired, may be mounted on the grounded side in or outside the circuitbreaker, since the concentration of the gaseous aggressive productswhich are found in the circuit breaker after the breaking operation isso small that said products do not appreciably affect the relevant partsthereof so that they are allowed to stay longer in the lowpressurecontainer of the circuit breaker. The powdered products are themselvesinsulators and since they cannot take up moisture under normalcircumstances they do not affect the insulating conditions within thecircuit breaker. The filters may be made much smaller than the knownfilters because instead of being located near the circuit contacts whichrequire them to be of such large size as is capable of handling the highmass rate of gas flow effected during circuit breaking, they are locatedremote from the circuit breaker and are not required to handle this highrate of gas flow. Instead, a filter if used effects its action at themuch reduced rate involved in returning the gas through the pump to thehigh-pressure container.

To realize the idea of the invention the surfaces of at least thosecircuit breaker parts which, during the switching-off process, come intocontact or are liable to come into contact with the arc may beconstituted by a sintered alloy of tungsten and nickel in the ratiolying between :5 percent and 99.710? percent. Under the influence of theelectric arc these alloys form with the dissociation products of theextinguishing gas extremely small quantities of permanently gaseoustungsten hexafluoride, which is aggressive only in cooperation withwater vapour, as well as powdered nickel fluoride which is insulating inits dry state and only slightly hygroscopic in the presence ofatmospheric water vapour contents. ln the presence of the very smallquantity of water vapour which during operation is contained in thecircuit breaker these products cannot appreciable affect the materialsand the insulating condition of the circuit breaker.

Advantageously, the surfaces of at least those circuit breaker partswhich, during the switching-off process, lie within the active radiationfield of the arc and/or of the very hot gas mixture produced bydissociation of a part of the heated extinguishing gas and/or come intocontact with said hot gas mixture are constituted by carbon. To that endthe metals used for the said circuit breaker parts may be covered with athin layer of carbon. Thencarbon is evaporated from said layer by theradiation and the thermal action of the electric arc and thedissociation products of the extinguishing gas and permanently gaseousfiuorinated carbon compounds are formed which are neither aggressive norhygroscopic, so that they need not be filtered out or discharged inanother manner.

The invention makes the provision of gas-blast circuit breakers in thementioned kind possible, of which the operation is stable and thedimensions are considerably reduced owing to the possibility of usingsmall filters or to omit same.

If the gas-blast circuit breaker constructed in accordance with theinvention comprises, as is usual, 21 first container for more compressedextinguishing gas, a second container for less compressed extinguishinggas, a switching chamber, through which said containers are incommunication with one another during the switching-off process only, aconduit connected to both containers, said conduit comprising a pump topump the extinguishing gas from the second container back to the firstone, and at least one filter to neutralize and and/or to collect theaggressive or otherwise injurious products formed by dissociation of theextinguishing gas and by the attack of materials used in the circuitbreaker by the disintegration products of said gas, said filter ispreferably mounted on the suction side of the pump whereat it may begrounded, beyond the pressure side of the pump in the second or thefirst container, or outside the circuit breaker. Then the replacement ofthe filter material is very much facilitated.

The invention will be elucidated with the aid of the drawing. In thedrawing: I

FIG. 1 is partly an axial sectional view, partly an elevational view ofa gas-blast circuit breaker constructed in accordance with theinvention; and

FIG. 2 is on a larger scale an axial sectional view of the switchingelement of said circuit breaker.

ln the drawing 1 designates an electrically grounded metal tank, inwhich an inner wall consisting of insulators 2, 3, 4 and contact rings5, 6 are provided. The space 7 between the tank and said inner wall isfilled with a gaseous, liquid, viscous or solid insulating material ofgreat dielectric strength. Mounted in the thus formed double-walledcasing is the switching element which is kept in place by insulators 8,9 and provided with electrically conductive contact holders 10, 11, Thelatter are electrically conductively connected with the contact rings 5,6 through connecting contact 12, 13. Connected to these contact rings 5,6 are the connecting conductors 14, 15 for the connection with the outercircuit. This circuit breaker serves only to break the circuit. To keepthe circuit interrupted and to close same an isolator switch (not shown)connected in series with this circuit breaker must be provided.

It appears from FIG. 2 that mounted between the contact holders 10, 11is a cooler made of perforated metal tubes 16, 17, 18, 19 and aninsulator 20. The contact holder supports an arc-extinguishing chamber22 surrounded by a metal wall 21 which is constricted at 23 and restswith a flange 24 upon the insulator 20. Said contact holder alsosupports a contact block 25 provided with resilient contacts 26 whichpermanently connect an axially movable switching rod 27 operated by anoperation mechanism (not shown) with the block 25. To makeand break thecircuit the switching rod 27 cooperates with a fixed contact supportedby the contact holder 11. This fixed contact consists of a contact block28 provided with resilient contacts 29. Mounted within said contactblock 28 is an axially movable arcing contact 31 which is loaded by aspring 30.

Provided in the wall 21 of the arc-extinguishing chamber 22 are severaldischarge openings 32 which, in the closed condition of the circuitbreaker, are closed by an annular sliding valve 33 mounted around saidwall 21. This annular sliding valve is opened by springs 34 during theswitching-off process and closed during the closing of the circuitbreaker by a ring 35 connected with the switching rod 27.

The circuit breaker is normally closed. In that condition the switchingrod 27, the arcing contact 31, the annular sliding valve 33 and the ring35 are in the positions shown in dotted lines. The circuit breakeroperates with an extinguishing gas consisting of one or more fiuorinatedcompounds, e.g. nexafluoride which, in the closed condition of thecircuit breaker, is contained in, the arc-extinguishing chamber 22 andin the circuit breaker spaces 36 and 37 under compression, say under apressure of atm. and in the circuit breaker spaces 38, 39 under lowercompression, say under a pressure of 3 atm. During the switching-offprocess the arcing contact 31 follows the switching rod 27 through apart of the switching stroke until the arcing contact is pushed againstthe stop'ring 40. Thereafter the switching rod 27 is removed from thearcing contact 31 and an electric are 41 is established. Just before theseparation of the switching rod and the'arcing contact the openings 32are opened, so that the extinguishing gas is able to flow with greatforce out of the extinguishing chamber 22 and, through the narrowopening 42, out of the circuit breaker spaces 36 and 37 to the circuitbreaker spaces 38, 39 to extinguish the electric arc. lmmediately afterthe extinction of the arc the circuit breaker is closed again and theused extinguishing gas is pumped by means of a pump 44 from the circuitbreaker spaces 38, 39 back to the circuit breaker spaces 36, 37 and thearc-extinguishing chamber 22 through a conduit 43 which is providedoutside the circuit breaker.

In accordance with the invention those parts which are liable to be hitby the arc, namely, the free ends of the switching rod 27 and the arcingcontact 31, the wall parts 45, 46, 47, 48 of the arc-extinguishingchamber and the upper surface 49 of the fixed contact 28, 29, are cladwith a layer 50 consisting of a sintered alloy of tungsten and nickel inthe ratio lying between 95:5 percent and 99.7103 percent whereas theremaining wall portions of the arc-extinguishing chamber and theremaining area of the upper surface of the fixed contact are covered bya layer of carbon 51. The reason for these covering layers is alreadyexplained heretofore.

Furthermore, filters 52 are provided in the conduit 43 to render theinjurious products produced by the switching process harmless and tocollect said products. These filters are also mounted outside thecircuit breaker, i.e.; on the electrically grounded side thereof, sothat they are accessible at any time. These filters may also bepositioned on the pressure side of'the pump in the conduit 43 or in thecircuit breaker spaces 39101137 near the bottom of the grounded tank 1.

c arm:

1. A gas-blast circuit breaker in which the electric are setup duringthe switching-off process in a region ofa switching andarc-extinguishing chamber is extinguished by a blast of gas forcedthrough said chamber and consisting of or comprising afluorine-containing compound, such as sulfur hexafluoride,

and in which at least all electricallyconductive solid partseonstituting wall surfaces bounding and facing said region of saidchamber are made from an alloy of -997 percent tungsten and 5-0.3percent nickel.

2. A gas-blast circuit breaker as claimed in claim 1, in whichelectrically conductive solid parts forming portions of the walls ofsaid switching and arc-extinguishing chamber and constituting wallsurfaces which adjoin said wall surfaces constituted by the saidtungsten-nickel alloy, are made from carbon.

3. In a gas-blast circuit breaker of the type including a bodypresenting a chamber, a pair of relatively movable contacts in saidchamber, means for opening said contacts whereby an arc is drawntherebetween, and means for blasting a flow of insulating gas throughsaid chamber to extinguish the are, the improvement wherein:

said insulating gas is a gas selected from the group consisting offluorinated compounds and mixtures thereof; and at least those portionsof said chamber and said contacts which are liable to be hit by the arcbeing constructed of a sintered tungsten-nickel alloy consistingessentially of from 95-997 percent tungsten and the balance nickel.

4. In the gas-blast circuit breaker according to claim 3 wherein saidinsulating gas is sulfur hexafluoride.

5. In the gas-blast circuit breaker as defined in claim 4 whereinsecondary portions of said chamber more remote from the arc are coatedwith carbon.

6. In the gas-blast circuit breaker as defined in claim 3 whereinsecondary portions of said chamber more remote from the arc are coatedwith carbon.

7. In the gas-blast circuit breaker as defined in claim-3 includingsupport bodies through which said contacts project, the surfaces of saidsupport bodies adjacent said contacts also being formed of said sinteredtungsten-nickel alloy.

8. In the gas-blast circuit breaker as defined in claim 7 whereinsecondary portions of said chamber and portions of said surfaces of thesupport bodies more remote from the are are coated with a carbon.

9. In the gas-blast circuit breaker according to claim 8 wherein saidinsulating gas is sulfur hexafluoride.

10. In the gas-blast circuit breaker as defined in claim 3 wherein saidbody includes inner wall portions defining first and second'chambers anda constricted portion joining said chambers, said constricted portionincluding a pair of oppositely directed frustoconical wall portionshaving their apices joined by a tubular wall portion, a contact supportin said first chamber including an end wall portion in spaced oppositionto one of said frustoconical wall portions and having one of saidcontacts projecting therefrom in axial alinement with said tubular wallportion but terminating in spaced relation thereto, the other of saidcontacts extending from said second chamber and through said constrictedportion into engagement with said one contact, a guide for said othercontact having an end wall disposed in spaced opposition to the other ofsaid frustoconical wall portions means for withdrawing said othercontact through said tubular wall portion to a position on the oppositeside thereof from said one contact whereby an arc is drawn between saidcontacts which is enclosed by said tubular wall portion, saidfrustoconical wall portions, said tubular wall portions, and said endwall portions being those portions of the chamber constructed of saidalloy.

11. In the gas-blast circuit breaker as defined in claim 10 wherein saidguide and said support include sidewall portions leading to said endwall portions thereof and which are constructed of graphite.

